1. Field of Invention
The present invention relates to a display device for displaying characters, numeric characters, patterns and so forth. In addition, the present invention relates to an electronic watch such as a wristwatch, a stopwatch and so forth for counting and displaying time.
2. Description of Related Art
Display devices for displaying numeric characters, characters and other information using a flat display device such as a liquid crystal display device have been widely known. In one such display device, as shown in FIG. 28 for example, as conventionally known, a pair of polarizers 102 and 103 are placed on both sides, respectively, of a liquid crystal panel 101, and a reflecting plate 104 is provided on the back of polarizer 103. The pair of polarizers 102 and 103 are placed so that, for example, the transmitted polarization axes form a right angle.
According to this conventional display device, display of information such as numeric characters or the like is effected by applying a predetermined voltage between electrodes of the liquid crystal panel 101. A region to which the voltage is not applied is a background of white or the like. In FIG. 28, the region to which the voltage is applied for displaying information is represented as "ON", and the background region to which the voltage is not applied is represented as "OFF".
In this display device, when the background is displayed (that is, the liquid crystal panel 101 is OFF), as shown by the arrow P, linearly polarized light of external light, i.e., natural light in the direction parallel to the plane of the drawing is transmitted by the polarizer 102. The polarization direction is twisted 90.degree. by the liquid crystal panel 101 in the OFF state to be changed to linearly polarized light in the direction perpendicular to the plane of the drawing. This linearly polarized light is irregularly reflected from the surface of the reflecting plate 104 after being transmitted by the polarizer 103. Then, a part of the irregular reflected light is displayed to the outside after being sequentially transmitted by the polarizer 103, the liquid crystal panel 101 and the polarizer 102. That part of the irregular reflected light is recognized as a reflection image of the reflecting plate 104, and normally, as a uniform white background.
When information such as numeric characters is displayed (that is, the liquid crystal panel 101 is ON), as shown by the arrow Q, linearly polarized light in the direction parallel to the plane of the drawing is taken out of the external light by the polarizer 102, and the linearly polarized light is transmitted by the liquid crystal panel 101. Since the liquid crystal panel is in the ON state at this time, the polarization direction of the linearly polarized light maintains the direction parallel to the plane of the drawing without being twisted. Therefore, the linearly polarized light is absorbed by the polarizer 103. Consequently, this portion is recognized from the outside as a dark color such as black.
According to the foregoing description, in this conventional display device, information such as numeric characters is displayed in a dark color, such as black, on the reflection image from the reflecting plate 104, which is a normally uniform white background.
In the above conventional display device, since two sheets of the polarizers 102 and 103 are respectively provided on both sides of the liquid crystal panel 101 and these polarizers have a function of absorbing linearly polarized light having a polarization axis other than a predetermined polarization axis, intensity of light guided to the outside for displaying information such as a background color and numeric characters and so forth is attenuated greatly. Therefore, there is a problem in that information such as numeric characters and the background are dark and hard to view.
In addition, since the background in the conventional display device is dark, even if various colors, patterns and other designs are added to the background, the patterns and so forth cannot be clearly recognized. Therefore, in the conventional display device, almost all of the backgrounds are displayed only in a single color such as white.
A conventional electronic watch has also been known having a structure such that a backlight is provided in place of a light-reflecting plate. According to the thus structured electronic watch, one of two forms can be selected to effect display: using the surface of the backlight as a light-reflecting layer, and using emitted light from the backlight. Usually, a reflection-type display form is selected during bright daytime, while a display form using the backlight is selected during dark nighttime.
In the above conventional electronic watch, however, there is a problem in that clocking contents of the electronic watch cannot be viewed under a dark environment such as nighttime and the like.
In addition, according to the above conventional electronic watch using the backlight, the backlight is large in size and a power source is required. Thus, there is a problem in that the electronic watch becomes large in size which causes inconvenience in handling and increase in cost.